Slack adjuster



Oct. 10, 1933.

G. P. BERRY sLAcK ADJUSTER l Filed March 28. 1932 .im 'm 2 Sheets-Shea?I 1 G. P. BERRY SLACK ADJUSTER Oct. 10, 1933.

2 Sheets-Shee't 2 Filed March 28. 1932 Patented Oct. 10, 1933 PATENT OFFICE SLACK ADJU STER George P. Berry, Detroit, Mich., assigner to General Motors Research Corporation, Detroit, Mich., a corporation of Delaware Application March 28, 1932. Serial No. 601,511

3 Claims.

This invention has to do with a slack adjuster for use in valve gear of internal combustion engines. It is shown embodied in a valve tappet but it is not essential that it be built into this part of the valve operating gear.

The invention is characterized by the fact that during each cycle of operation of the valve gear, slack is introduced into the system and adjustment is thereafter made to take up the excess slack but, unlike previous constructions, these operations occurduring the period when the valve is seated. During the opening and closing movements of the valve the parts of the slack adjuster are locked so that the valve operating mechanism acts as a rigid assembly.

lin the drawings:

Figure iis a sectional view through portion ci an i head engine showing the application of my invention thereto.

Figure 2 -is a' view identical with Fig. 1 but showing the parts in a diiferent position.

Figure 3 is a view on line 3-3 of Figure 1.

Figure 4 is a section through the nut embodied in the slack adjuster.

Figure 5 is an elevation of the nut.

Figures 6 and 7 show various methods of mounting the rotary wear plate onthe bottom ci" the tappet.

Figure 8 is a view corresponding to Figure i, showing a modined construction.

Referring -irst to `Figures 1 to 4, 10 indicates a portion oi a camshaft provided with a cam l2 grcoved as at 14. The bottom surface 16 of the groove is of conventional cam shape. The cam l2 is distinguished from conventional cams in that it is cut away between the points 18 and 20 so that its surface is inside the base circle, this circle being indicated at 22.

My improved slack adjuster is built into the tappet. lThe part 24 may be termed the tappet proper. It is provided upon its bottom face with a rotatable disc 26 held in place by bushing or 'ferrule 28 which passes througha central aperture in the tappet and is riveted over as at 30 upon the inner surface of the bottom of the tappet. It is also prevented from rotating by means of spring pressed ball 25 operating in longitudinal slot 27. The purpose of the rotatable disc 26 is A to distribute the wear resulting from the rubbing action of the cam. A coil spring 35 surrounds the tappet 24 and yieldingly holds the tappet in engagement with the cam 12. Within the bushing 28 is slidably mounted plunger 32 which may be provided with shoulder 34 limiting its extension from the lower end of the bushing 28.

.d icated in Figure 2. vHere the cutting away'of The lower end of the plunger 32 rides in the groove 16 in the cam. 'Ihe upper end of the plunger-32 is of greater diameter and may have a sliding flt in the interior of the tappet 24. There issupported upon the plunger a nut 36 having 60 one end closed by cap 37 which may have a pressed fit in the nut. There is interposed between plunger 32 and thev cap 37 suitable antifriction devices to facilitate rotation of the nut.

I have illustrated a ball39. The nut 36 is prefer- 65 ably split as at 38 and has threaded engagement with screw 40 upon which the lower end of valve stem 41 rests. For best operation the thread should have a self-locking angle. The nut 36 is provided with a conical surface 42 engaging a 70 similar surface formed in the interior of the tappet 24. The lower end of the nut 36 is provided with a helical slot 44 inclined to its axis, and this slot receives the end of pin 46 fixedly secured in the` adjacent wall of the tappet 24. .A torsion spring 48 has one end secured in the nut 36, and` the other end secured to the screw 40 by anysuitable means. 1 have preferred to show the upper end of the spring received in a slot formed in the end of the screw.

This device operates as follows: During the opening and closing of the valve the cam i2 exerts its thrust against the disc 26 on tappet 24, and the tappet transmits the thrust through the engaging conical surfaces 42 to the nut 36. $5 The provision of the conical surfaces, in com-- bination with the splitting of the nut causes the nut to,grip the screw 40, adding to the` locking action resulting from the use of threads of selflocking angle. The tapered surfaces 42 are of 90 such angle that they remain locked together even though the thrust of the valve be momentarily removed. As .a consequence during the entire period of opening and closing of the valves the tappet, from the disc 26 to the nut 40, acts as a 95 rigid thrust transmitting member.

Shortly after the tappet reaches the base circle of the cam the parts vassume the position inthe cam 12 at 18-20 has permitted the tappet 100 24 to drop further ldown, and this action may be assured by the`use of a spring such as shown at 35. The plunger 32 dose not follow the tappet 24 as its end is engaged by the bottom 16 of the 105 groove 14 in the cam and consequently the nut 36 and screw 40 remain in the same position relative to the valve. As a consequence the conical surfaces 42 disengage and the nut 36 is rotated slightly as a consequence of the pin 46 110 secured to the tappet 24 engaging the side walls of the helical slot 44 in nut- 36.

Let it be assumed that the slopes of the screw thread and of helical slot 44 are such that rotation of the nut 36 tends to project the screw 40 out of the nut when the screw is prevented from rotating with the nut.

The forces tending to prevent the screw rotating with ,the nut are (1) the relatively weak force of the torsion spring 48 which is continually tending to rotate the screw in the reverse direction and (2) the friction between the screw and the valve stem. The forces tending to cause the screw and nut to rotate together are (1) the friction between the threads of the screw and nut and (2) the force of the valve spring acting at the mechanical disadvantage supplied by the screw threads for if the nut is to have independent rotation it must project the screw out of the nut and raise the valve against the resistance of its spring. Since the second set of forces is greater, the screw and nut will rotate together and sliding will take place between the nut and the end of the valve stem.

When the tappet 24, in following the cut away portion of the cam 12, reverses its movement, the pin 46 and slot 44 will rotate the nut in a reverse direction, tending to retract the screw n into the nut. If it be assumed that the valve is slightly oiI its seat as a result of expansion of the parts during the last cycle of operation, the nut will rotate independently of the screw allowing the valve to seat. The only opposing forces are friction between the screw threads and the force of the weak spring 48 and these are insufficient to prevent this action. If the valve is seated and after it has seated as just described, further rotation of the nut will introduce slack into the system but -this slack will be taken upv 4i()l as fast as it is introduced by spring 48 advancing the screw.

By providing for positive introduction of slack into thesystem during each cycle of valve operation, seating of the valve is assured and it is not possible for the valve to be wedged off its seat by the slack takeup mechanism.

Further rotation of the cam results in engagement of the conical surfaces 42, and the nut 36 is contracted about the screw and the parts lift of the cam.

The device will operate equally satisfactorily by reversing the directions of the screw thread and cam slot, the only difference being that the described actions willtake place in reversed sequence.

'Ihe use of the split nut 42 not only producesa rigid train of .elements during the operating portion of the cycle but also makes it possible to employ threads of angles larger than those that would ordinarily be self-locking.

In Figures 6 and '7 I have shown further modiflcations of the mounting of the disc 26.' In'the modification shown in Figure the disc 26' is provided with a anged peripheryV engaging the edges of the lower end of the tappet.` In Figure 'I the disc 26" is provided with an integral tubular extension 50 locked to the bottom of the tappet by any suitable means, such as spring ring 52.

In the modiiication shown in Figure 8, the tappet 54 is permitted to rotate, and there is interposed between the tappet and the nut 36 an intermediate member 56 having conical surface 58 cooperaing with the conical surface 42' formed f7.5. on the nut.` `The intermediate member 56 may from are again locked into a rigid unit ready for thel be supported on ball thrust bearing 60. The intermediate member 56 is held against rotation by ball 62 spring-pressed into longitudinal slot 64. The pin 46, secured in the intermediate member and having its end engaged in slot 44 functions in a manner similar to the pin 46 in slot 44 of the nrst form of the invention. The operation of this modiication is the same as that of the ilrst form of the invention except that the tappet itself is capable of rotation instead of being provided with a rotatable shoe.

My improved slack adjuster has the great advantage that on the operating stroke the tappet acts as a rigid member of a ilxed length and is not extensible should the thrust be momentarily removed. VThis is accomplished by the positive gripping of screw 40 by the split nut 36 as a result of the action of the conical surfaces 42. Since the slack adjusting mechanism is inoperative when the valve is being moved, there is no opportunity for it to take up slack in case of bouncing of the valve or other irregular movement or failure of the valve mechanism to follow the cam. Hence there is no possibility of the slack adjusting mechanism holding the valve off`1'00 its seat. When, however, the valve is closed the clutch action of the nut 36' is disabled, and the action of the pin 46 in the slot 44 in combination with the torsion spring 48 produces the desired increase in slack, and subsequent taking up oi slack. This new adjustment allows for expansion or contraction of the parts, and also for wear and pounding of the valve into its seat so that the valve gear is always quiet, and need not be adjusted at any time throughout its life.

If desired the cam 16, shown in Figures 1, 2, 3 and 8, may be of circular contour concentric with the axis of the camshaft. This will probably be found desirable because it will' reduce contact of the cam and plunger 4to a 1 I claim:

1. Valve mechanism comprising a plurality of extensible parts, means operative only during a portion of the cycle of movement of the mechanism for moving said parts to open and close thevalve, means comprising a locking member for locking said parts against extension, said means coming into operation at the end of the non-operating portion of the cycle and continuing in operation throughout said operating portion of the cycle, means for releasing said locking means after the termination of the operating portion of the cycle, means rendered operative by release of said locking means for thereafter adjusting said extensible members to take up slack, or introduce slack into the system, said locking means being operative at the end of the operating cycle for locking said parts against extension so that the parts form an unyielding inv extensible train of mechanism during the operating portion of the cycle.

2..Valve mechanism comprising a plurality ofy parts having intertting cam faces so that upon rotation of said parts with respect to each other their overall v length is increased or diminished, yielding means tending to produce relative rotation of said parts in a direction to increase their overall length, means operative only during a portion of the cycle of movement of the mechanism for moving said parts to open and close the valve, means comprising a locking member for locking said parts against relative rotation, said means coming into operation at the end of the non-operating portion of the cycle and continuing-in operation throughout said operating :,asaaor portion of the cycle, means for releasing said locking means after the termination of the operating portion of the cycle, means rendered operative by release of said locking means for rotating one of said parts in a direction tending to introduce' slack into the system, whereupon said yielding means becomes operative to rotate said members in a direction to increase their overall length and take up slack in the system, said locking means being operative at the end of the operating cycle for locking said parts against extensioniso that the parts form an unyielding inextensible train of mechanism during thev operating portion of the cycle.

3. Valve mechanism comprising a poppet valve, a spring for holding the poppet valve on its seat, a tappet for operating the valve comprising a screw and a nut, thevnut being split to yieldingly grip the screw and having an outer gripping surface, a spring tending to unscrew said members .to extend their overall length, a. sleeve surrounding the nut and having a surface adapted to grip the surface on the'nut to lock it against rotation, a c'am for operating the sleeve to raise ,the nut and screw and open the valve, said cam having a portion of the non-operating part of its periphery cut away to permit the sleeve to drop away from the nut to release it for rotation, means rendered operative by release of said locking means for thereafter adjusting said extensible members to take up. slack or introduce slack into the system, said cam being provided with a groove having a circular bottom over the portion of its periphery corresponding to the cut away portion of the cam, and means supported on the bottom of the groove supporting said nut when the sleeve drops away from it.

GEORGE P. BERRY. 

